The present invention relates to the technical field of combustion chambers for gas turbine engines. Its particular subject is the chamber bottom. Its final subject is a gas turbine engine such as a turbojet fitted with such a combustion chamber.
In all of the following, the terms “axial”, “radial”, “transverse” correspond respectively to an axial direction, to a radial direction, and to a transverse plane of the engine, the terms “upstream” and “downstream” correspond respectively to the direction of flow of the gases in the engine.
A conventional divergent combustion chamber is illustrated in FIG. 1, which is an axial section showing a half of the combustion chamber, the other half of the latter being deduced by symmetry relative to the axis of the engine (not shown). The combustion chamber 110 is housed in a diffusion chamber 130 that is an annular space defined between an outer casing 132 and an inner casing 134, in which a compressed comburant, ambient air, originating upstream of a compressor (not shown) is inserted via an annular diffusion duct 136.
This divergent combustion chamber 110 comprises two concentric walls, one outer 112 and the other inner 114, that are coaxial and substantially conical. The walls flare out from upstream to downstream. The outer wall 112 and inner wall 114 of the combustion chamber 110 are connected together, toward the upstream of the combustion chamber, by a chamber bottom 116.
The chamber bottom 116 is a frustoconical annular part which extends between two substantially transverse planes while flaring out from downstream to upstream. The chamber bottom 116 is connected to each of the two walls, outer 112 and inner 114, of the combustion chamber 110. The chamber bottom 116 is slightly conical. It is furnished with injection systems 118 through which injectors 120 pass that insert the fuel at the upstream end of the combustion chamber 110 where the combustion reactions take place.
These combustion reactions have the effect of causing heat to radiate from downstream to upstream in the direction of the chamber bottom 116. Therefore in operation the chamber bottom is subjected to high temperatures. In order to protect it, sectorized heat screens, also called baffles 122, are placed between the center and the walls of the chamber bottom. These baffles 122, one of which is represented in FIG. 3, are substantially flat plates attached by brazing to the chamber bottom 116 with a central opening 122a for the injection system to pass through. They comprise two low lateral walls 122b 122c along the radial edges, turned toward the wall of the chamber bottom and two air guidance tongues 122e 122f along the transverse edges turned toward the center and arranging a space with the inner, respectively outer, walls 114 and 112 of the chamber. The baffles are cooled by the impacts of cooling air jets entering the combustion chamber 110 through cooling orifices 124 pierced in the chamber bottom 116. The air forming these jets, flowing from upstream to downstream, is guided by chamber fairings 126, passes through the chamber bottom 116 through the cooling orifices and comes to impact the upstream face of the baffles 122. The air is then guided radially toward the inside and outside of the center in order to initiate the film for cooling the walls 114 and 112 respectively.
This guidance along the baffles is ensured by the radially-oriented lateral low walls. These low walls also have a sealing function. Being in contact with or providing a minimal clearance with the chamber bottom, they prevent the air from mixing between two adjacent baffles, entering the center and disrupting the combustion. These disruptions have an impact on pollution and are to be avoided. Specifically, the performance in discharge of pollutants, CO and CHx, are capable of being harmed by the undesirable insertion of this cold air particularly when the engine is idling when the clearance is greatest.